The composite semipermeable membrane is called an RO (reverse osmosis) membrane, an NF (nanofiltration) membrane, or a FO (forward osmosis) membrane, depending on the filtration performance and treatment method of the membrane, and such membrane can be used for the production of ultrapure water, seawater desalination, desalination of brackish water, waste water recycling treatment, or the like.
As a composite semipermeable membrane that is frequently used industrially, for example, there is mentioned a composite semipermeable membrane wherein a skin layer containing a polyamide resin obtained by reacting a polyfunctional amine component with a polyfunctional acid halide component is provided on the surface of a porous support. In general, the skin layer surface of the composite semipermeable membrane has a negative charge due to the influence of the carboxylic acid remaining in the polyamide resin. Therefore, when water (for example, sewage) containing an ionic organic contaminant such as a surfactant is treated with the composite semipermeable membrane, the organic contaminant is adsorbed on the skin layer surface by electrostatic attraction and water permeability is gradually reduced, which is a problem.
In order to solve the above problems, for example, Patent Document 1 has proposed a reverse osmosis composite membrane in which a surface layer of a separation active layer is coated with a polyvinyl alcohol that is an electrically neutral organic polymer insoluble in water of 25° C. and soluble in water of 80° C. and has a saponification degree of 99% or more.
In addition, Patent Document 2 has proposed a reverse osmosis membrane to which a cationic polymer is attached and then an anionic polyvinyl alcohol is attached.
On the other hand, as a fluid separation element conventionally used for reverse osmosis filtration, ultrafiltration, microfiltration and the like, for example, there is known a spiral wound separation membrane element in which a unit consisting of a feed spacer for guiding a feed-side fluid to the surface of a separation membrane, a separation membrane for separating the feed-side fluid, and a permeate spacer for guiding to a core tube a permeation-side fluid that has passed through the separation membrane and is separated from the feed-side fluid is wound around a perforated core tube (Patent Documents 3 and 4).